Hillary Clinton is poised to have one of the biggest nights of her career.

Clinton could sweep up enough delegates Tuesday to give her an all-but-insurmountable lead for the Democratic presidential nomination over Vermont Senator Bernie Sanders. The 11 states holding contests put about a third of the required delegates on the table.

Precincts are scheduled to close at 7 p.m. Eastern time in Georgia and Virginia, where surveys have showed Clinton with an overwhelming advantage, as well as in Sanders’s home state of Vermont. Voting ends an hour later in Massachusetts, Oklahoma, Alabama, Tennessee and most of Texas, with results rolling in later from the Democratic contests in Arkansas, Minnesota and Colorado.

Clinton has dominated the race since Sanders essentially tied her in the Iowa caucuses Feb. 1 and defeated her by more than 22 percentage points a week later in New Hampshire. She won the Nevada caucuses Feb. 20 in the first test in a state with a large minority population, and won the South Carolina primary Feb. 27 by almost 48 percentage points.

Southern States

After winning 86 percent of the black vote in South Carolina, Clinton is expected to dominate contests in Southern states with a similar electorate. Black voters comprise half the electorate in Georgia and Alabama and roughly a quarter of Democrats in Virginia, Arkansas and Tennessee, according to exit polls published by ABC News on its website. Hispanic voters account for 30 percent of Democrats voting in Texas, the exit polls showed.

In recent interviews, Sanders has said he expects to win Vermont and hopes to do well in the primaries in Massachusetts and Oklahoma, as well as the caucuses in Minnesota and Colorado, where he’s made several stops in the past two weeks. Speaking to reporters Monday night, Sanders also said he expects to do better than expected in Texas, the state with the most delegates at stake.

Starting Ahead

Yet Clinton starts with a lead in delegates. Because they are awarded in Super Tuesday states on a proportional basis based on vote percentages, even a Sanders victory in some states won’t narrow the delegate gap if the races are close, said Joe Trippi, a Democratic strategist who isn’t aligned with either candidate.

“It’s going to be a really bad night for Sanders,” Trippi said.

Clinton can effectively secure the nomination as soon as the results from Super Tuesday are in, and certainly no later than mid-March, said Jeff Berman, the campaign’s consultant for delegate strategy.

Berman helped Barack Obama beat Clinton with delegate math in the 2008 race. After serving as first lady to a popular Democratic president and as a senator from New York, Clinton was the favorite, only to be overtaken by Obama’s insurgent campaign. Clinton entered this year’s race having learned the lesson of not taking her opponent -- or any individual contest -- for granted.

States in which Clinton is expected to do well Tuesday are worth 571 delegates combined. By comparison, Colorado and Minnesota, two states with caucuses where Sanders could prevail, have only 143 together. Massachusetts has 91 delegates, Oklahoma 38 and Sanders’ home state of Vermont has only 16.

Superdelegates

Clinton also has an advantage among the party’s 712 so-called superdelegates, a mix of elected officials and party leaders who are free to back whom they like and change their loyalties.

“A realist could well feel after Super Tuesday that Sanders won’t be able to catch up,” Berman said.

Sanders, a self-professed socialist, vowed Tuesday to campaign all the way to the Democratic National Convention in Philadelphia in July, relying on a message about an economy rigged to favor the rich.

“We are very proud of what are doing, we’re proud of what we’re going to continue to do,” Sanders told voters early Tuesday morning as he and his wife, Jane, voted in Burlington. “If there is a larger voter turnout today across this country we are going to do well. If not, we’re probably going to be struggling.”

Turning to Republicans

While Clinton has said she is still focused on Sanders, she has begun to turn her focus to Republican front-runner Donald Trump.

“If I’m fortunate enough to be the Democratic nominee, the sooner the better,” Clinton said Tuesday on the Tom Joyner radio show. “The sooner we can turn our attention to what the Republicans stand for and what they’re saying and their bigotry. We’ve got to get into it and we’ve got to make sure that we don’t let that happen to our country.”

Carrie Kennedy, a 59-year-old independent in Austin, Texas, said she made a last-minute decision to vote for Clinton today after previously planning to vote for Trump because “he says what a lot of people want to say.” She was turned off by Trump’s initial failure to repudiate the support of former Ku Klux Klan leader David Duke in a weekend interview, she said.

“I didn’t like the mud-slinging by the Republican candidates,” she said. “Some of it is getting into the sewage. It’s really distasteful.”

In Virginia, turnout by mid-afternoon in Arlington County, which comprises the western suburbs of Washington, was 24 percent, according to the county Elections office. Of those, 61 percent were Democrats and 38 percent were Republicans. As in all of Virginia, voters there can choose either party’s ballot no matter which party they belong to.

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Sanders has invested staff resources in states and continues to draw large crowds, including 6,500 on Sunday in the university town of Fort Collins. He’s also managed to keep drawing contributions. His campaign said Tuesday that he raised $42 million in February, about double the amount he took in the week before. By comparison, Clinton raised $14.9 million in January. Her campaign hasn’t released figures for February.

To keep pace, Sanders spent $6 million on broadcast TV and national cable commercials during the past week, compared with $7.7 million by Clinton, according to data Tuesday from Kantar Media’s CMAG, which tracks political ads.

But with non-white voters accounting for more than 40 percent of the Democratic electorate in states voting after the initial nominating contests, Sanders hasn’t shown he can appeal to minorities, said Steve Elmendorf, a Democratic strategist in Washington who was deputy campaign manager for presidential candidate John Kerry and is backing Clinton.

The former secretary of state has relied on her longstanding ties to the black community, lingering goodwill from the economic advances during her husband’s presidency and a strong pitch that she would carry on the initiatives of Obama, the first black chief executive.

“I do not see any evidence that Sanders has figured out how to break her lock on African-American voters,’’ Elmendorf said.